It is known that 4-oxo-4H-pyrido[1,2-a]pyrimidine derivatives have analgesics and other effects influencing the central nervous system (British Patent No. 1,209,946, U.S. Pat. No. 4,291,036 and German Patent No. 2,414,751). One of the most advantageous representatives of these compounds is 1,6-dimethyl-3-ethoxycarbonyl-6-methyl-4-oxo-4H-pyrido[1,2-a]pyrimidinium methosulfate [Arzneimittelforschung 22, 815 (1972)] used as an analgesic drug in clinical practice. Other derivatives have been shown to exert a preferable antiarteriosclerotic (German Patent No. 2,705,775), antiallergic and antiasthmatic (Belgian Patent Nos. 873,192 and 873,194), antiinflammatory [German Patent Nos. 2,728,198 and 2,526,983; Arzneimittelforschung 29, 766 (1979)], cardiovascular [Sankyo Kenkyusho Nempo 29, 75 (1977)] and selective serotonine-2 receptor-blocking (U.S. Pat. No. 4,342,870) effects. The antiulcer action of tetrahydro- and hexahydro-4-oxo-4H-pyrido[1,2-a]pyrimidine-3-carboxylic acid derivatives have also been reported [Drugs Exptl. Clin. Res. 11, 493 (1985); ibidem 13, 253 (1987)]. Some unsaturated 4-oxo-4H-pyrido[1,2-a]pyrimidine-3-carboxylic acid derivatives showed an analgesic action which, however, could not be utilized because of the hydrolytic instability of the bicyclic moiety [Magyar Kemikusok Lapja 31, 281 (1976)].